BLOOD. 
The specific gravity of human blood is, at 
a medium, 1.05. Mr. Fourcroy found the 
specific gravity of bullock’s blood, at the 
temperature of 60°, to be 1.056. The 
blood does not uniformly retain the same 
consistence in the same animal, and its con- 
sistence in different animals is very various. 
It is easy to see that its specific gravity 
must be equally various. When blood, 
after being drawn from an animal, is allowed 
to remain for some time at rest, it very 
soon coagulates into a solid mass, of the 
consistence of curdled milk. This mass 
gradually separates into two parts, one of 
which is fluid, and is called sernrn ; the 
other, the coagulum, has been called cruor, 
because it alone retains the red colour 
which distinguishes blood. This separation 
is very similar to the separation of curdled 
milk into curds and whey. The proportion 
between the cruor and serum of the blood 
varies much in different animals, and even 
in the same animal in different circum- 
stances. The most common proportion is 
about one part of cruor to three parts of 
serum. 1. The serum is of a light greenish 
yellow colour : it has the taste, smell, and 
feel of the blood, but its consistence is not 
so great. It converts Syrup of violets to a 
green, and therefore contains an alkali. On 
examination, Roulle found that it owes this 
property to a portion of soda. When heat- 
ed to the temperature of 156°, the serum 
coagulates. It coagulates also when boiling 
water is mixed with it, but if serum be 
mixed with six parts of cold water, it does 
not coagulate by heat. When coagulated, 
it has a greyish white colour, and is not un- 
like the boiled white of an egg. If the co- 
agulum be cut into small pieces, a muddy 
fluid may be squeezed from it, which has 
been termed the serosity. After the sepa- 
ration of this fluid, if the residuum be care- 
fully washed in boiling water and examined, 
it will be found to possess all the properties 
of coagulated albumen. The serum, there- 
fore, contains a considerable proportion of 
albumen. Hence its coagulation by heat, 
and the other phenomena which albumen 
usually exhibits. If serum be diluted with 
six times its weight of water, and then 
boiled to coagulate the albumen, the liquid 
which remains after the separation of the 
coagulum, if it be gently evaporated till it 
becomes concentrated, and then be allowed 
to cool, assumes the form of a jelly. Con- 
sequently it contains gelatine. If the co- 
agulated serum be heated in a silver vessel, 
the surface of the silver becomes black, 
heing converted into a sulphuret. Hence 
it is evident, that it contains sulphur ; and 
Proust has ascertained that it is combined 
with ammonia in the state of a hydrosulphu- 
ret. If serum be mixed with twice its weight 
of water, and, alter coagulation by heat, the 
albumen be separated by filtration, and 
the liquid be slowly evaporated till it is 
considerably concentrated, a number of 
crystals are deposited when the liquid is 
left standing in a cool place. These cry- 
stals consist of carbonate of soda, muriate 
of soda, besides phosphate of soda and 
phosphate of lime. The soda exists in the 
blood in a caustic state, and seems to be 
combined with the gelatine and albumen. 
The carbonic acid combines with it during 
evaporation. Thus it appears that the se- 
rum of the blood contains albumen, gela- 
tine, hydrosulphuret of ammonia, soda, 
muriate of soda, phosphate of soda, and 
phosphate of lime. These component 
parts account for the coagulation occasion- 
ed in the serum by acids and alcohol, and 
the precipitation produced by tannin, ace- 
tate of lead, and other metallic salts. The 
cruor, or clot, as it is sometimes called, is 
of a red colour, and possesses considerable 
consistence. Its mean specific gravity is 
about 1.245. If this cruor be washed care- 
fully, by letting a small jet of water fall 
upon it, till the water runs off colourless, it 
is partly dissolved, and partly remains upon 
the searce. Thus it is separated into two 
portions : namely, 1. A white, solid elastic 
substance, which has all the properties of 
fibrin ; 2. The portion held in solution by 
the water, which consists of the colouring 
matter, not, however, in a state of purity, 
for it is impossible to separate the cruor 
completely from the serum. We are in- 
debted to Bucquet for the first precise set 
of experiments on this last watery solution. 
It is of a red colour. Bucquet proved that 
it contained albumen and iron. Menghini 
had ascertained, that if blood be evapo- 
rated to dryness by a gentle heat, a quan- 
tity of iron may be separated from it by 
the magnet. The quantity which he ob- 
tained was considerable ; according to him, 
the blood of a healthy man contains above 
two ounces of it. Now, as neither the serum 
nor the fibrin extracted from the cruor 
contains iron, it follows of course, that the 
water holding the colouring matter in solu- 
tion must contain the whole of that metal. 
This watery solution gives a green colour to 
syrup of violets. When exposed to the air, 
it gradually deposits flakes, which have tire 
